Process of sweetening hydrocarbon distillates



Patented Nov. 17, 19 31 UNITED STATES PATENT OFFICE THOMAS B. KIMBALL,OF MARTINEZ, CALIFORNIA, ASSIGNOR TO SHELL OIL COMPANY, OF SANFRANCISCO, CALIFORNIA, A CORPORATION OF CALIFORNIA PROCESS OF SWEETENINGHYDROCAIRJBON DISTILLATES No Drawing.

This invention relates generally to a process or method of removingsulphur compounds from hydrocarbons. It has special application forremoving sulphur compounds 5 from gasoline obtained by the crackingprocess.

It is an object of this invention to devise an eli'ective and economicalprocess for the removal of sulphur compounds, particularlymercaptans,'from hydrocarbon distillates.

It is a further object of this invention to devise a novel process forsweetening hydrocarbon distillates, and improving their doctor test.

it is another object of this invention to increase the effectivenessofprocesses for removal of sulphur from normally liquid hydrocarbons bytreating the hydrocarbon while in the vapor phase.

.a Further objects ofthis invention will appear from the followingdescription in which I have set forth the preferred embodiment of myinvention. It is to be understood that the appended claim is to beaccorded a range or" chemical equivalents. consistent with the state ofthe prior art Certain hydrocarbon distillates which are normally in theliquid phase, such as gasoline and kerosene, and particularly those 0distillates resulting from the oil cracking process, are rendered sourand unfit for sale by the presence of sulphur compounds. A large part ofthese sulphur compounds are mercaptans, which must be removed to sweetenthe product. It has previously been proposed to remove these compoundsby contacting the liquid hydrocarbon with caustic soda or other alkalineliquid. This treatment is not entirely efiective since it leaves asubstantial amount of the sulphur compounds in the distillate, and maynot sweeten it sufliciently to effect a negative doctor test. As thedoctor test is aflected largely by the presence of mercaptans, it isapparent that they are not removed to a practical extent by treatmentwith caustic soda solution while the hydrocarbon is in the liquid phase.

In this invention, treatment of hydrocarbons with an alkaline solutionis made much more effective by contacting it with vapors Applicationfiled May 31, 1927. Serial No. 185,598.

of the-hydrocarbon. The process is carried out in practice by passingthe vapors of the hydrocarbon thru a scrubbing tower thru which ismaintained a counter flow of an alkaline solution, preferably an aqueoussolution of caustic soda. The treating solution is maintained at atemperature which is above the temperature of condensation of thehydrocarbon vapors, so that liquefaction will not occur. The mercaptansand'other sulphur compounds in the hydrocarbons combine with the causticsoda to form non-volatile compounds which are carried away by thetreating solution. The temperature of the treating agent should notbecome sufiiciently high to cause its substantial vaporization, as thismight result in the separation of solids out of the treating liquid.

The treatment of hydrocarbon while in the vapor phase effects resultsfar superior to treatment while in the liquid phase. By actual analysis,gasoline treated while in the liquid phase still contained from 0.16 to.20 percent sulphur compounds and was still positive to the doctor test.When the same hydrocarbon was treated by my process, the sulphurcompound content was reduced to about 0.06 percent and the doctor testwas negative or sweet.

The process of my invention is particularly useful in treatinglightgasoline such as absorption gasoline or pressure distillate tops.These gasolines have a series of relatively low boilings points; thus atleast 90% of the liquid asoline will boil at less than 100 6., theboiling point of water. The boiling point at the 90% point, as found bythe usual distillation test conducted on gasoline of this character, was90 C. on one of the gasoline treated in accordance with my process.

In treating distillates of this light character, 1 preferably utilize analkaline solution having a boiling point substantially above the 90%point of the gasoline. In one instance I have employed a 16 B sodasolution containing about 11% NaOH or 12.5 parts on 100 parts of waterso that the boiling point of the solution lies between 100105 C.,averaging about 103 0. While a. slight portion of the heavier fractionsof the gasoline being treated may be condensed, the fighter fractions,constituting the-ma or portion of the line, remain vaporized during thetreatmg. Because of the effect of partial pressures a slight amount ofthe solution evaporates. However, due to the differences in the vaporpressures of the solution and the gasoline, and since the alkalinesolution is preferably maintained below its boilin point, this amountisslight and does not e ect the operation of the process as a whole.

I claim:

The process of sweetening cracked light petroleum distillates containingmercaptans to reduce the sulphur content to substantially 0.06 per centor below comprising: treating unsweetened cracked petroleum distillatescontaining mercaptans, by counter-currently scrubbing said distillateswith a liquid aqueous solutlon of caustic soda, while maintaining saiddistillates in the vapor phase, whereby mercaptans are removed from thevapors by the formation of non-volatile compounds in said liquid aqueoussolution, said aqueous solution bein substantially below its boilingpoint, and su stantially above the condensation temperature of saidvapors, under the ressure condition of the system and removmg thedistillate in the vapor phase from contact with the liquid aqueoussolution containing the non-volatile compounds.

In testimony whereof, I have hereunto set my hand.

THOMAS B. KIMBALL.

